.\" Copyright (c) 1990, 1991, 1993
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.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.\" @(#)atexit.3 8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/stdlib/atexit.3,v 1.10 2002/12/18 13:33:03 ru Exp $
.\"
.Dd May 20, 2008
.Dt ATEXIT 3
.Os
.Sh NAME
.Nm atexit
.Nd register a function to be called on exit
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn atexit "void (*func)(void)"
#ifdef UNIFDEF_BLOCKS
.Ft int
.Fn atexit_b "void (^block)(void)"
#endif
.Sh DESCRIPTION
The
.Fn atexit
function
registers the function
.Fa func
to be called at program exit, whether via
.Xr exit 3
or via return from the program's
.Fn main .
Functions so registered are called in reverse order;
no arguments are passed.
#ifdef UNIFDEF_BLOCKS
.Pp
The
.Fn atexit_b
function is like
.Fn atexit
except the callback is a block pointer instead of a function pointer.
.Bd -ragged -offset indent
Note: The
.Fn Block_copy
function (defined in
.In Blocks.h )
is used by
.Fn atexit_b
to make a copy of the block, especially for the case when a stack-based
block might go out of scope when the subroutine returns.
.Ed
#endif
.Pp
These callbacks must not call
.Fn exit ;
if it should be necessary to terminate the process while in such a
function, the
.Xr _exit 2
function should be used.
(Alternatively, the callbacks may cause abnormal
process termination, for example by calling
.Xr abort 3 . )
.Pp
At least 32 callbacks can always be registered;
more are allowed as long as sufficient memory can be allocated.
.\" XXX {ATEXIT_MAX} is not implemented yet
.Sh RETURN VALUES
#ifdef UNIFDEF_BLOCKS
.ds ATEXIT_B atexit_b
#endif
.Rv -std atexit \*[ATEXIT_B]
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ENOMEM
No memory was available to add the function to the list.
The existing list of functions is unmodified.
.El
.Sh SEE ALSO
.Xr exit 3
.Sh STANDARDS
The
.Fn atexit
function
conforms to
.St -isoC .